Bed shear-stress under combined waves and currents on smooth and rough beds (TR 137)

Soulsby, R.L. and Clarke, S. (2005) Bed shear-stress under combined waves and currents on smooth and rough beds (TR 137). Technical Report. HR Wallingford, Wallingford.

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Abstract

Produced within Defra project FD1905 (EstProc). Calculations and numerical modelling of the erosion, transport and deposition of sediments in estuaries and coastal areas rely heavily on expressions that contain the bed shear-stress, representing the friction exerted by the flowing water on the bed. In general the bed shear-stress is generated by the combined effects of waves and currents, whose turbulent boundary layers interact non-linearly. The flow is usually considered to be hydrodynamically rough turbulent for sand and gravel beds, and hydrodynamically smooth turbulent for freshly-deposited mud beds. Most existing theories and models for the wave-current-interaction have considered only the rough bed case, and they have generally been too complicated and computer-intensive to be usable in whole-estuary (or coastal) models. This report produced within Defra project FD1905 (Est Proc) describes the development and testing of a new method of calculating the mean, maximum and root-mean-square bed shear-stresses due to combined waves and currents. The method caters for rough turbulent and smooth turbulent (and also laminar) flows, with the greatest emphasis on the less well-researched smooth turbulent case. Tests of the new method against published data for smooth flows gave better agreement than existing methods. The new method is also simpler, being expressed as explicit algebraic equations that are computationally fast. A detailed algorithm giving the “recipe” to implement the method is given in an appendix.

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